2. z CYBRID
• Cybrid (cytoplasmic hybrid): Cybrids are cells
or plants containing nucleus of one species but
cytoplasm from both the parental species.
• Cybridization: production of somatic cybrid. The
process of protoplast fusion resulting in the
development of cybrid is known as cybridization.
3. • Gleba 1979 fused tobacco protoplast which produced a
cybrid.
• Melchers and Labib in 1974 fused protoplast of two
haploid light sensitive lines of Nicotiana tabacum.
• Kao and Wetter in 1976 isolated cell cybrids of Glycine
max and Nicotiana glauca .
• Pental and Cocking proposed that triploids could be
produced by fusing protoplast isolated from microspores
at the tetrad stage (n) of a species with protoplast isolated
from the somatic cells of other species.
• Pirrie and Power synthesized triploids by fusing
microspore protoplast of Nicotiana glutinosa with somatic
cell protoplast of Nicotiana tabacum .
4.
5. • Cybrids are produced during fusion of protoplast from
two phylogenetically distant species.
• Regeneration from phylogenetically distant species will have
plastomes from both parental species but the functional
genome of only one species through chromosomal
elimination.
• The extranuclear genes which control agronomically
important characters are of considerable interest.
6. • Nuclear genome of one parent “donar” is inactivated
chemically or with irradiation before protoplast fusion.
• Irradiation with x-rays or gamma rays ,in doses of 50 to
300 Gy, is effective in partial or complete inactivation of
donar cells.
• Fusion of untreated “recipient” protoplast with “donar”
and culturing result in cybrid plants possessing the
nucleus of the “recipient” and the cytoplasm of both
parental species.
• Phylogenetically distant species produce cybrids during
protoplast fusion.
7. • Fusion between protoplasts of potato
(Solanum tuberosum) and tomato
(Lycopersicon esculentum) has created
pomato (Solanopersicon, a new genus).
• 2. Interspecific fusion of four different species
of rice (Oryza brachyantha, O. eichngeri, O.
officinalis and O. perrieri) could be done to
improve the crop.
• Cybrids are important for the transfer of
cytoplasmic male sterility (CMS), antibiotic
and herbicide resistance in agriculturally
useful plants.
8. The cybrid produced by electrofusion between Citrus unshiu
and C. sinensis.
Restoration of male fertile Nicotiana by fusion of protoplast
derived from two different cytoplasmic male sterile cybrids.
Correct deficiencies of nitrate reductase and xanthium
dehydrogenase activities in tobacco by fusing its normal
protoplast with protoplast of Physalis and Datura
inactivated by x-ray treatments.
Streptomycin resistance has been transferred from
Nicotiana tabacum to three other species of tobacco.
9. • Two different parental genomes that cannot reproduce
sexually (asexual or sterile) are recombined.
• Overcomes sexual incompatibility barriers.
• Used in study of cytoplasmic genes & their activities- plant
breeding experiments.
• To transfer cytoplasmic male sterility (tomato,tobacco).
• To transfer antibiotic resistance character(tobacco)
• To transfer herbicide resistance (brassica)
• Used in mitochondrial research.
Advantages
10. • Biparental inheritance of cytoplasm during sexual reproduction
occurs in only a few genera .
• Plant regeneration from protoplasts is often a difficult, or
even impossible task.
• Instability of transferred genes in somatic hybrids.
• Recovering controlled asymmetric hybrids due to factors like
cell fusion, nuclear fusion, nuclear genes segregation and
recombination.